Some of the training materials that you could use for JN0-102 are:
1. Juniper official training books from Education Services (which is sold by onsecure):
https://junipertraining.onfulfillment.com/SubCategory.aspx?d=62&sd=94&sm=94
2. You should download the free Junos Genius app for practicing with flash cards, learning from learnings bytes and more
3. O'reily books on enterprise routing, enterprise switching and security can be used for various learning certification track
4. Virtual or on site training from Juniper certified partners can be taken. There are multiple ones offering courses.